Tip: updating a negative list (such as looking for "script", "sCrIpT", "ßCrîpt", etc) will require expensive and constant deployments and will always fail as attackers work out your list of "bad" words. Positive validation is simpler, faster and usually more secure and needs updating far less than any other validation mechanism.

Tip: Consider the use of a "governor" to regulate the maximum number of requests per second / minute / hour that this user may perform. For example, a typical banking user should not perform more than ten transactions a minute, and one hundred per second is dangerous and should be blocked.

Tip: Only certain personally identifiable information and sensitive values MUST be encrypted. Encrypt data that would be embarrassing or costly if it was leaked or stolen.

Tip: It is best to encrypt data on the application server, rather than the database server.

Design:

Tip: Do not use RDBMS database, row or table level encryption. The data can be retrieved in the clear by anyone with direct access to the server, or over the network using the application credentials. It might even traverse the network in the clear despite being "encrypted" on disk.

Use octet byte streaming instead of providing access to real files such as PDFs or CSVs or similar.

Ensure every page requires a role, even if it is "guest".

Pre-render:

Validate user is authenticated.

Validate role is sufficient to view secured URL.

Render:

Send CSRF token.

Validate user is authenticated.

Validate role is sufficient to perform secured action.

Validate CSRF token.

Tip: It's impossible to control access to secured resources that the web application server does not directly serve. Therefore, PDF reports or similar should be served by the web application server using binary octet streaming.

Tip: Assume attackers will learn where "hidden" directories and "random" filenames are, so do not store these files in the web root, even if they are not directly linked.